U.S. patent application number 09/130561 was filed with the patent office on 2001-07-19 for multilayer barrier shrink film.
Invention is credited to MOGENSEN, STEVEN A., STALL, ALAN D..
Application Number | 20010008660 09/130561 |
Document ID | / |
Family ID | 22445258 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008660 |
Kind Code |
A1 |
STALL, ALAN D. ; et
al. |
July 19, 2001 |
MULTILAYER BARRIER SHRINK FILM
Abstract
A multilayered packaging film includes a first exterior layer of
a heat sealable polymer and second exterior layer on a side
opposite from the first exterior layer, and including two inner
layers made of polyvinylidene chloride disposed between the first
and second layers and an innermost core layer disposed between the
two inner layers wherein the innermost core layer is not
crossed-linkable when exposed to radiant energy.
Inventors: |
STALL, ALAN D.; (NAPERVILLE,
IL) ; MOGENSEN, STEVEN A.; (LAKEVILLE, MN) |
Correspondence
Address: |
KINNEY & LANGE,P.A.
THE KINNEY & LANGE BUILDING
312 SOUTH THIRD STREET
MINNEAPOLIS
MN
554151002
|
Family ID: |
22445258 |
Appl. No.: |
09/130561 |
Filed: |
August 7, 1998 |
Current U.S.
Class: |
428/35.4 |
Current CPC
Class: |
B32B 2327/00 20130101;
B32B 27/304 20130101; B32B 2323/046 20130101; B32B 2307/7242
20130101; B32B 2439/70 20130101; Y10T 428/1341 20150115; B32B 27/08
20130101; B32B 27/32 20130101 |
Class at
Publication: |
428/35.4 |
International
Class: |
B32B 001/02 |
Claims
1. The multilayered packaging film comprising: a first exterior
layer comprising of a heat sealable polymer on one side and a
second exterior layer on an opposite side, and two inner layers
comprising polyvinylidene chloride between the first and second
exterior layers and an innermost core layer disposed between the
two polyvinylidene chloride layers wherein the innermost core layer
is not cross-linkable when exposed to radiant energy.
2. The film of claim 1 wherein the innermost core layer is made of
a polypropylene ethylene copolymer.
3. The film of claim 1 wherein the heat seal layer is made of an
ultra low density polyethylene.
4. The film of claim 1 wherein the heat seal layer is made of an
ethylene vinyl acetate polymer.
5. The film of claim 1 wherein the heat seal layer is a combination
of very low density polyethylene and ethylene vinyl acetate.
6. The film of claim 1 wherein the second layer is made of a ultra
low density polyethylene.
7. The film of claim 1 wherein the second exterior layer is made of
an ethylene vinyl acetate polymer.
8. The film of claim 1 wherein the second exterior layer is made of
a combination of an ultra low density polyethylene and an ethylene
vinyl acetate polymer.
9. The film of claim 2 wherein the innermost core layer includes an
ethylene acid co-polymer combined with a polypropylene
co-polymer.
10. The film of claim 1 wherein the first exterior layer comprises
approximately 40% of the thickness of the film, the second exterior
layer comprises approximately 20% of the thickness of the film, the
first and second inner polyvinylidene chloride layers each
comprises approximately 6% of the thickness of the film and the
innermost core layer comprises approximately 20% of the thickness
of the film.
11. A package made of a multilayered film comprising: a first
exterior layer comprising of a heat sealable polymer on one side
and a second exterior layer on an opposite side; two inner layers
comprising polyvinylidene chloride between the first and second
exterior layers; and an innermost core layer disposed between the
two polyvinylidene chloride layers wherein the innermost core layer
is not cross-linkable when exposed to radiant energy.
12. The film of claim 11 wherein the innermost core layer is made
of a polypropylene ethylene copolymer.
13. The film of claim 11 wherein the heat seal layer is made of an
ultra low density polyethylene.
14. The film of claim 11 wherein the heat seal layer is made of an
ethylene vinyl acetate polymer.
15. The film of claim 11 wherein the heat seal layer is a
combination of very low density polyethylene and ethylene vinyl
acetate.
16. The film of claim 11 wherein the second layer is made of an
ultra low density polyethylene.
17. The film of claim 11 wherein the second exterior layer is made
of an ethylene vinyl acetate polymer.
18. The film of claim 11 wherein the second exterior layer is made
of a combination of an ultra low density polyethylene and an
ethylene vinyl acetate polymer.
19. The film of claim 12 wherein the innermost core layer includes
an ethylene acid co-polymer combined with a polypropylene
co-polymer.
20. The film of claim 11 wherein the first exterior layer comprises
approximately 40% of the thickness of the film, the second exterior
layer comprises approximately 20% of the thickness of the film, the
first and second inner polyvinylidene chloride layers each
comprises approximately 6% of the thickness of the film and the
innermost core layer comprises approximately 20% of the thickness
of the film.
Description
BACKGROUND OF THE INVENTION
[0001] This invention generally relates to multilayer barrier
shrink films and to bags made therefrom. More particularly, a
multilayer barrier film or bag is provided having at least two core
layers of a PVDC gas barrier material and at least one core layer
of a propylene-ethylene random copolymer. The present invention is
especially well-suited for vacuum packaging situations where
toughness, resistance to puncture, and high shrink values are
important, such as in packaging meat cuts, including those
containing protruding bone portions.
[0002] Polymeric films are well known for packaging applications,
approximately half of which are currently food packaging
applications which address the perishability of foods. Foods are
especially vulnerable to degradation upon exposure to oxygen.
Refrigeration, thermal processing after packaging, reduction of
water content and the like are practiced to varying degrees and in
varying combinations in order to reduce degradation of foods and
food products. A very effective approach in this regard is to cover
or envelope the food item with a polymeric film containing a
so-called barrier layer. Barrier layers are known to prevent oxygen
from reaching the product.
[0003] Another concern, especially when working with food packaging
applications, is attempting to eliminate residual oxygen contained
inside the food package. One popular method which has been
practiced with a view toward eliminating residual oxygen is to
package the film-enveloped food inside a vacuum chamber where a
substantial quantity of oxygen has been evacuated. The film
therefore clings tightly to the outside surface of the product when
the thus packaged product is re-exposed to air after packaging.
Subsequent spraying or immersion of the package in hot water causes
the film to shrink tightly around the product, providing it with an
especially wholesome aesthetic appearance, while keeping food
juices and the like tightly retained inside the package and
avoiding or minimizing the collection of liquid in gaps and
crevices in the packaging and between the packaging and the
product.
[0004] It is well known to co-extrude films to produce a multilayer
product useful in these types of applications. Included are film
products which have been biaxially oriented to thermally expand the
film, allowing for future retraction by heat. Films of this type
have been processed into a bag and used on evacuation equipment for
vacuum packaging of various products, including food products and
bone-in meat products or other items having grossly irregular
surfaces. Multilayer heat shrinkable films in this regard include
those described in U.S. Pat. No. 2,762,720, where a multilayer film
of 80% polyvinylidene chloride (PVDC) is combined with 20% of
another polymeric material such as polyethylene terephthalate (PET)
for providing added mechanical strength and enhanced
appearance.
[0005] Also included in the background art are U.S. Pat. No.
3,022,543 and No. 3,567,539, which illustrate a system for
extruding laminate successive layers. This approach includes
irradative cross-linking of the innermost layer, a polyolefin, and
subsequent reheating and laminating to it a PVDC intermediate layer
and then an outer polyolefin layer, preferably ethylene vinyl
acetate (EVA) having a vinyl acetate content of 3% to 28%. The
entire composite thus constructed is then reheated in a hot water
bath, biaxially oriented, and wound on a reel as a flattened tube.
The tube is stretched 100% in the machine and in the transverse
directions. Tubes of this type can be made into bags on
conventional bag-making machinery.
[0006] Biaxial orientation enhancement has been known to be
practiced by a so-called double bubble approach. In approaches such
as those of U.S. Pat. No. 3,278,663, No. 3,456,044 and No.
3,555,604, all of which are incorporated herein by reference, a
first bubble is blown to carry out an initial biaxial orientation.
A secondary bubble is also created, with infrared heaters being
used. Bubble quenching is practiced using suitable quenching
approaches such as cold air ring sprays. U.S. Pat. No. 4,188,350
and No. 4,196,240 propose a biaxially oriented film using
polyethylene-polypropylene blends with an Ionomer such as Surlyn
1650 as a core layer, no barrier being proposed. Various other
films are proposed as being suitable for biaxial orientation and
provide heat shrinkability useful in certain applications.
[0007] As further background, films are known to have been
irradiated, including before biaxial orientation. Included in this
regard are U.S. Pat. No. 4,044,187 and No. 4,104,404. Biaxially
orientable films are proposed having multiple layers such as a
four-layer structure as in U.S. Pat. No. 4,207,363 and up to
five-layer structures as in U.S. Pat. No. 4,457,960.
BRIEF SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, important advances
in multilayered barrier shrink films and bags are provided. the
multilayered film has at least five functional layers. The inside,
product-contacting layer is referred to herein as the heat seal
layer. The outside layer, which is visible to the potential
purchaser or the bagged product, is referred to herein as the abuse
layer. The intermediate layers or core layers positioned between
the heat seal layer and the abuse layer are referred to herein as
the shrink layers, the barrier layers, or the shrink/barrier
layers. An adhesive layer typically will be positioned between all
or some of the functional layers. The multilayered film is
biaxially oriented and irradiated.
[0009] In an important aspect of this invention, the innermost core
layer does not cross-link during this irradiation procedure, while
the other functional layers do respond to the irradiation. Thus,
the multilayered barrier shrink film is non-irradiated in the sense
that it is not significantly affected by the irradiation applied to
the totality of the film, while the remainder of the functional
film layers are fully irradiated. In this regard, the innermost
core layer is preferably a propylene ethylene copolymer (PER),
either alone or in combination with another component or other
components. It is also an important aspect of this invention that
at least two barrier core layers include polyvinylidene chloride
(PVDC). It is also preferred that the seal layer and abuse layer
include an ultra density polyethylene (ULDPE), or in situations
where abuse is not as great a concern, ethylene vinyl acetate (EVA)
can be substituted for or combined with the ULDPE, in combination
with additional components if so desired in certain instances.
DETAILED DESCRIPTION
[0010] Multilayered coextrusions in accordance with the present
invention incorporate a minimum of five functional layers, suitably
adhered together, typically by an interspersed adhesive layer or by
an adhesive included within one or more of the working layers.
Considering the product-contacting layer of the coextrusion to be
an inside, heat seal layer, the outside or external layer is an
abuse layer, while the coextrusion contains three or more
shrink/barrier layers therebetween.
[0011] The present invention includes a new approach in coextruded
multilayered film polymers having superior vacuum conformance
properties and which offer excellent protection, both from physical
abuse and from transference of gases such as oxygen therethrough.
There is a need for packaging film and bags which exhibit barrier
protection and mechanical strength and abuse protection, while
possessing the ability to shrink so as to tightly envelope, closely
follow, and not be damaged by a wide range of contours, including
those which are relatively sharp, upon shrinking, such as those
presented by bone-in meat cuts and the like.
[0012] With more particular reference to the innermost core layer,
this includes as a primary component or as the only component
thereof a polymer which will not significantly crosslink when the
multilayer barrier shrink film is subjected to irradiation.
Included in this regard are polymers including polypropylene, which
also exhibits the property or reasonably good adherence to the
shrink/barrier layer. It also exhibits the additional advantage of
providing a good barrier to fat and/or grease transmission.
[0013] A preferred innermost core layer according to the present
invention is a propylene-ethylene copolymer (PER). Such a PER
should be a random copolymer in order to allow the polypropylene
component to properly adhere to the shrink layer. In this regard,
the randomness index is preferably approximately 0.5, while the
melt flow is typically approximately 1.7 grams per 10 minutes. The
innermost core layer should have a high isotactic molecular
structure and should have a melt flow of about 1.5 to about 10
decigrams per minute. A PER component of the innermost core layer
should have a relatively low ethylene content, typically not
greater than about 6% ethylene on a weight basis preferably not
greater than about 5% ethylene on a weight basis. These types of
PER materials will not crosslink upon irradiation. Typical
manufacturers of PER materials are Exxon Corporation of Irving,
Tex.; Millenium Chemicals, Inc. of Iselin, N.J.; Phillips Chemical
Co. of Houston, Tex. and Montell of Hoofdorp, Netherlands.
[0014] With further reference to the inner most core layer, same
can be composed entirely of a PER material. It can also be blended
with other components when particular properties are desired. Such
other components include specialty polyethylenes such as linear low
density polyethylene (LLDPE) and ultra density polyethylene
(ULDPE). Elastomeric properties can be enhanced by blending into
the innermost core layer materials such as polybutylene or
ethylene-butene copolymer. Examples of elastomers which can be
included within the innermost core layer are ethylene-propylene
copolymers or other types such as Vistalon.RTM. 702 from Exxon
Corporation, or Telcar.RTM. 303 from B F Goodrich Company of
Richfield, Ohio. Such elastomers can be included at a level of
about 10% of the inside heat seal layer, thereby promoting
adhesion. Adherence to the intermediate shrink/barrier layers can
be provided by or enhanced by the inclusion of a suitable adhesive
as generally discussed herein as a component blended with the
innermost core layer. Typically, blends of such components in this
or other layers are physical mixtures which are preblended and flow
into a single extruder feed location.
[0015] When it is desired to reduce crystallinity of the PER in the
innermost core layer, ethylene acid copolymer (EAA) can be blended
thereinto. Typically, such an addition will allow easier bubble
blowing, improve optics and improve adhesion. Other materials for
blending with PER in the innermost core layer include
ethylene-methyl acrylate blends, such having elastomeric
properties, good adhesion, thermal stability and compatibility with
materials such as EVA, PVDC and EAA. PER can also be blended with
butene-ethylene copolymers.
[0016] Referring now to the barrier core layers, these include the
material PVDC in particular for its barrier to moisture and more
particularly for its barrier to gases. Importantly, a synergistic
improvement in moisture barrier of the entire structure is obtained
by dividing a similar amount of PVDC material into two layers as
opposed to the use of a similar amount of material in just one
layer. More importantly, a synergistic improvement in gas barrier
of the entire structure is obtained by dividing a similar amount of
PVDC material into two layers as opposed to the use of a similar
amount of material in just one layer. A suitable PVDC is MA Saran,
available from Dow Chemical Company of Midland, Mich., other
suppliers being Kureha Chemical Industry Co., Ltd. of Japan and
Solvay of Brussels, Belgium, as well as Dow MA 123 Saran, MA 119
Saran and MA 127 Saran made by Dow Chemical Company. Such materials
exhibit toughness and durability.
[0017] Referring now to the seal layer and abuse layer, these
include a material which provides stabilized stretching, improved
heat stability, resistance to oils, improved seal strength in the
presence of oils, and helps to improve biaxial orientation and to
broaden the application temperature range. Preferred in this regard
are ultra low density polyethylene (ULDPE) materials. ULDPE
materials tend to be somewhat expensive, but do not adhere well to
certain materials such as polyvinylidene chloride (PVDC) or
hydrolyzed ethylene vinyl acetate (EVOH). Typical ULDPE materials
are Affinity PL-1840 and PL-1845 made by Dow Chemical Company of
Midland, Mich. The former has a melt flow of 1.0 decigrams per
minute, with 9.5% octene comonomer. Generally speaking, ULDPE
polymers are polyolefins that provide high impact and puncture
resistance. Because of the poor adherence of ULDPE materials to
many of the materials of the multilayer film, adhesive layers or
additives may be needed in order to achieve the necessary adherence
between the ULDPE-containing layer and the adjacent layer. ULDPE
materials provide a further advantage of exhibiting excellent
hot-tack, with the result that the seal is strong even before it is
cooled, which is particularly advantageous for shrink bags, where
seals need to be made on a film enclosure or bag which is changing
in dimension.
[0018] When it is desired to reduce costs, the seal layer and abuse
layer can include EVA to replace some of the ULDPE materials. ULDPE
material offers good printability for outside indicia, and it
contributes good clarity to this layer. Another component which can
be included in the seal layer and abuse layer is a specialty
polyethylene such as an ionomer. Ionomers have the important
advantage of enhancing blowability.
[0019] A typical EVA when present in the abuse layer or in the
shrink layer has a low melt flow, such as 0.3 dg/min, which is
typical of Dupont.RTM. 3135 made by E. I. DuPont De Nemours and
Company of Wilmington, Del. When included within the heat seal
layer, EVA should be of a higher melt flow in order to better
promote adhesion, such a heat flow being on the order of 0.7
dg/min, typical of Dupont.RTM. 3165 and Union Carbide.RTM. 6833
made by Union Carbide of Danbury, Conn. With respect to the vinyl
acetate content of the EVA component, when included, Dupont.RTM.
3135 has a VA content of 12%. The higher VA content EVA's have an
increased low temperature heat stability, resilience, flexure
resistance, impact resistance, toughness, coefficient of friction,
clarity and abrasion resistance. It is important that the VA
content not be too high so as to cause burn through on seals during
packaging with the heat sealing equipment. Alternatives are LLDPE
polymers, which offer similar heat sealability and flexibilities as
do 4% to 18% EVA copolymers. A typical LLDPE is an ultra low
density polyethylene having densities below 0.915 g/cc.
[0020] PVDC normally has poor adhesion to ULDPE materials, and
mixing ULDPE with EVA improves this adhesion. Further improvement
in this regard is available by adding an adhesion additive such as
Dupont.RTM. CXA 3101 or CXA 1104 to the mixture, for example.
Alternatives include Plexar 5298 from Millenium Chemicals, Inc. In
those situations where polypropylene contacts PVDC or EVA, adhesion
enhancers also can be used, such as DuPont.RTM. CXA 3101 or CXA
1202. Adding CXA adhesive resin provides a high melt index and a
low melt viscosity component. Particularly suitable is blending
with DuPont.RTM. 3135 EVA, which has a 0.35 melt index and a 12% VA
content.
[0021] With further reference to the adhesive layers, an adhesive
layer will preferably be present between each of the heat seal
layer and the shrink/barrier layer, as well as between the
shrink/barrier layer and the abuse layer. A discrete adhesive layer
can be omitted in the event that adequate adhesive component is
present in one of the layers, such as the heat seal layer to allow
for adequate adhesion to the adjacent layer, for example the
shrink/barrier layer. Adhesive can also be omitted in those
situations where the adjoining layers adhere well to each other,
such as when the shrink/barrier layer is PVDC and the abuse layer
is EVA or a large percentage of EVA. A typical suitable adhesive is
low density polyethylene adhesive. An example is Admer.RTM. LF 500
from Mitsui Petrochemical Industries, Ltd. of Tokyo, Japan.
[0022] In the coextruded film, it is usually important that the
inside heat seal layer be the thickest layer, typically accounting
for about 40-60% of the coextrusion, usually 50-60%. The barrier or
core layer typically makes up about 10-20% of the coextrusion,
while the outside, abuse layer makes up about 15-355 of the
coextrusion. A typical adhesive layer accounts for about 3-5% of
the coextrusion. The final film will have a total thickness of
between about 50-90 microns (about 2-3.8 mils).
[0023] Once the various layers are coextruded, they are quenched
biaxially oriented, and then annealed slightly using infrared heat.
Preferably, the film is rechilled after annealing, followed by
irradiation. Preferably, the irradiation takes place while the film
is on a reel, the dosage being between about 2 and 10 megarads.
Exemplary equipment in this regard is Electron Beam Curing
equipment available from RPC of Hayward, Calif., or ESI of Woburn,
Mass.
[0024] Annealing procedures as discussed herein are useful in
controlling the flatwidth of the coextrusion more precisely.
Flatwidth control is useful when the coextrusion includes Ionomer
component(s). With this approach, approximately 5% of the flatwidth
is annealed out of the coextruded film. This allows more accurate
gauge control. Such annealing can be practiced using infrared heat.
It is especially preferred that the annealing be carried out with a
small quantity of nitrogen trapped between squeeze rolls in order
to thereby inflate the film and prevent any film-to-film
adhesion.
[0025] Exemplary illustrations of the disclosure herein are
provided in the following examples.
EXAMPLE 1
[0026] A blend of approximately 60% PER and 40% polybutylene are
introduced into the innermost core extruder (about 21/2 inches
diameter, 24:1 L/D ratio) of a known double bubble extrusion line,
with water quench. This is for forming the innermost core layer.
The next layer for the coextrusion equipment is pure elastomeric
adhesive, using a 3/4 inch extruder. The outer shrink/barrier layer
or core layer is made of Dow.RTM. MA Saran plasticized PVDC, such
core layer being 1 inch, 20:1 L/D. The outer layer of coextrusion
extrudes ULDPE plus EVA blend through a 11/2 inch, 24:1 L/D
extruder. Towards the inside, the next layer for the coextrusion
equipment is pure elastomeric adhesive, using a 3/4 inch extruder.
The inner shrink/barrier layer or core layer is made of Dow.RTM. MA
Saran plasticized PVDC, such core layer being 1 inch, 20:1 L/D. The
inner layer of coextrusion extrudes ULDPE plus EVA blend through a
21/2 inch, 24:1 L/D extruder. With this set up, extrusion
thicknesses are as follows. The inside heat seal layer composes
approximately 40% of the structural thickness, each adhesive layer
composes about 4% of the structural thickness of the coextruded
film, each barrier core layer composes 6% of the coextruded film,
the innermost core layer composes 20%, and the outer, abuse layer
makes up about 20% of the coextrusion. Each thickness can vary plus
or minus 25%, depending upon specific resins and intended
applications for the coextruded multilayer barrier shrink film. The
extruder runs a 3 inch primary flatwidth, approximately 50 mils
thick, at approximately 30 feet per minute. An internal powder is
sprayed on the inside during extrusion, and quenching is carried
out using a series of spray rings emitting chilled water.
[0027] The resulting coextrudate is quenched, but kept warm
(approximately 100.degree. F.) to ensure the primary web is not
crystallized, but is amorphous for reblowing. The web is conveyed
upwardly into a known biaxial orientation unit, where infrared heat
is applied using a series of rotating heater bands. The primary web
is heated above the glass transition temperatures of all of the
resins, and a secondary biaxial orientation is effected. the
secondary web is blown to about 14 inches, and the line speed of
the exiting nip roll is about 130 feet per minute. The primary web
thins out to about 2.5 mil thickness. The film is completely
quenched exiting the secondary heater stack using dry air, chilled
to 40.degree. F. the product is then reheated using infrared, and
annealed, with a trapped bubble of nitrogen or dry air in between
two squeeze rolls, to a 13 inch width. The resulting final product
is recooled and wound on a surface wound reeler.
[0028] The resulting film is allowed to sit in cold storage for two
days to thermally stabilize and crystallize. The film is then taken
to a commercial electron beam curing unit, where it is irradiated
to crosslink all but the PER layer, with a dosage of about 4
megarads. The thus prepared product is then wound, with inflation
prior to winding to ensure gases evolved during crosslinking are
not entrained in the film.
[0029] After treatment and a sitting time of about one day, the
film is printed if desired. Whether or not printed, the film is
converted into bags on a commercial bag machine. The bags may be
monogrammed on the bag machine for identification. The bags are
then chilled in a cooled warehouse in order to achieve final
stabilization of the multilayer barrier shrink film bags.
EXAMPLES 2-18
[0030] Multilayer barrier shrink film is prepared generally in
accordance with the procedure described in Example 1, with
variations in the resins passed into and through the coextruder.
These different resins are listed as follows:
1 Heat Seal Intermediate Innermost Intermediate Abuse Example
(Inside) Core Adhesive Core Adhesive Core (Outside) 2 ULDPE + PVDC
Adhesive + PER Adhesive + PVDC ULDPE + EVA EVA EVA EVA 3 ULDPE +
PVDC Adhesive + PER + Adhesive + PVDC EVA + EVA EVA LLDPE EVA
Ionomer 4 ULDPE PVDC Adhesive PER Adhesive PVDC ULDPE EVA EVA 5
ULDPE + PVDC Adhesive PER Adhesive PVDC ULDPE + EVA EVA 6 ULDPE +
PVDC Adhesive + PER + Adhesive + PVDC ULDPE + EVA EVA ULDPE EVA EVA
7 ULDPE + PVDC Adhesive PER + Adhesive PVDC ULDPE + Ionomer
polybutylene + Ionomer adhesive 8 EVA + PVDC EVA PER + EVA + EVA
PVDC EVA + Ionomer adhesive Ionomer 9 ULDPE + PVDC Adhesive + PER +
ULDPE Adhesive + PVDC ULDPE + EVA EVA EVA EVA 10 ULDPE + PVDC EVA
PER + EVA PVDC ULDPE + EVA polybutylene + EVA adhesive 11 ULDPE +
PVDC Adhesive PER + Adhesive PVDC ULDPE + EVA Ionomer EVA 12 ULDPE
+ PVDC Adhesive + PER + Adhesive + PVDC ULDPE + EVA EVA Ionomer EVA
EVA 13 ULDPE + PVDC Adhesive PER + Adhesive PVDC ULDPE + EVA EVA
EVA 14 ULDPE + PVDC Adhesive + PER Adhesive + PVDC LLDPE + EVA EVA
EVA Ionomer + EVA 15 ULDPE + PVDC Adhesive + PER Adhesive + PVDC
ULDPE + EVA LLDPE LLDPE EVA 16 ULDPE + PVDC Adhesive + PER Adhesive
+ PVDC ULDPE + EVA ULDPE ULDPE Ionomer 17 ULDPE + PVDC Adhesive +
PER Adhesive + PVDC ULDPE + EVA ULDPE ULDPE EVA + Ionomer 18 ULDPE
+ PVDC Adhesive + PER + Adhesive + PVDC ULDPE + EVA EVA ethylene
EVA EVA butene copolymer
[0031] It will be understood that the embodiments of the present
invention which have been described are illustrative of some of the
applications of the principles of the present invention. Numerous
modifications may be made by those skilled in the art without
departing from the true spirit and scope of the invention.
[0032] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *